Synthesis of Azadioxa-Planar Triphenylboranes Bridged by Aryl- and Alkylimino Groups and Their Photophysical Properties.

Heteroatom-bridged planar triphenylboranes, in which the three phenyl groups are bridged at the ortho positions by heteroatoms, are attracting growing attention as one of the heteroatom-containing π-conjugated molecules. Herein, we developed the synthetic method of planar triphenylboranes bridged by two oxygen atoms and one nitrogen atom, and the substituent on the nitrogen atom is derived into various aryl and alkyl groups. A key intermediate bearing an imino group (-NH-) was synthesized from a bis-triflate precursor bridged by two oxo groups via a nucleophilic aromatic substitution reaction of benzyl amine and following debenzylation. The X-ray crystallographic analysis revealed that the compound exhibits a planar molecular structure which can form a one-dimensionally π-stacked structure. The photophysical and density functional theory studies revealed that their highest occupied molecular orbitals and lowest unoccupied molecular orbitals (LUMOs) are originated from the triphenylborane moiety, while introducing strong electron-withdrawing groups such as the 4-cyanophenyl group on the nitrogen atom can induce the localization of the LUMO at the aryl groups instead of the triphenylborane moiety.

1,2,4-Triazol-3-ylidenes with an N-2,4-dinitrophenyl substituent as strongly π-accepting N-heterocyclic carbenes.

The synthesis and characterisation of a series of new Rh and Au complexes bearing 1,2,4-triazol-3-ylidenes with a N-2,4-dinitrophenyl (N-DNP) substituent are described. IR, NMR, single-crystal X-ray diffraction and computational analyses of the Rh complexes revealed that the N-heterocyclic carbenes (NHCs) behaved as strong π acceptors and weak σ donors. In particular, a natural bond orbital (NBO) analysis revealed that the contributions of the Rh→Ccarbene π backbonding interaction energies (ΔEbb ) to the bond dissociation energies (BDE) of the RhCcarbene bond for [RhCl(NHC)(cod)] (cod=1,5-cyclooctadiene) reached up to 63 %. The Au complex exhibited superior catalytic activity in the intermolecular hydroalkoxylation of cyclohexene with 2-methoxyethanol. The NBO analysis suggested that the high catalytic activity of the Au(I) complex resulted from the enhanced π acidity of the Au atom.

Investigation of the Lewis acidic behaviour of an oxygen-bridged planarized triphenylborane toward amines and the properties of their Lewis acid-base adducts.

Lewis acid behavior of an oxygen-bridged triphenylborane (1) to amines and the properties of Lewis acid-base adducts of 1 with amines have been investigated. UV-vis titration and 11B NMR experiments showed the formation of Lewis acid-base adducts of 1 with pyridine, DMAP, quinuclidine, and DABCO, respectively (1·amine). X-ray crystallographic analysis revealed that the planar shape of 1 was converted to a bowl shape by the formation of 1·amine. Interestingly, 1·quinuclidine, 12·DABCO, and 1·DABCO exhibited dual emissions. Excitation spectra and photoluminescence decay time measurements suggest that the dual emissions were ascribed to two excited species, i.e., [1·amine]* and [1]* generated by photodissociation in the excited states.

Nitrogen-directed ortho-selective homocoupling of aromatic compounds catalyzed by ruthenium complexes.

A nitrogen-directed regioselective homocoupling reaction of aromatic compounds has been found to be catalyzed by a ruthenium complex in the presence of methallyl acetate as a hydrogen scavenger.

Direct C-H bond arylation of arenes with aryltin reagents catalysed by palladium complexes.

Direct C-H bond arylation of simple arenes with aryltin reagents has been successfully catalysed by PdCl2 in the presence of CuCl2. CuCl2 proved to be an activator for a palladium intermediate as well as an oxidant.

The first synthesis and X-ray crystallographic analysis of an oxygen-bridged planarized triphenylborane.

An oxygen-bridged planarized triphenylborane has been successfully synthesized. X-ray crystallographic analysis revealed that the molecule has a complete planarized structure and the shortest C-B bonds among the triarylboranes synthesized to date.

Ruthenium-catalyzed arylation of 2-alkenylpyridines with aryl bromides: alternative E,Z-selectivity to Mizoroki-Heck reaction.

Regio- and stereoselective arylation of 2-alkenylpyridines with aryl bromides is catalyzed by specific Ru(II)-phosphine complexes affording beta-arylated (Z)-2-alkenylpyridines, in which the aryl moiety is introduced cis to the pyridyl group. This geometrical selectivity is in sharp contrast to the Mizoroki-Heck reaction. [reaction: see text]

Conjugate addition of organosiloxanes to alpha,beta-unsaturated carbonyl compounds catalyzed by a cationic rhodium complex.

[reaction: see text] A novel, additive-free, and clean conjugate addition reaction of organosiloxanes to alpha,beta-unsaturated carbonyl compounds catalyzed by a cationic rhodium complex in water-containing solvent has been developed. A plausible reaction mechanism involving the additive-free transmetalation step between the rhodium complex and the silicon reagent is proposed.

Ruthenium complex catalyzed direct ortho arylation and alkenylation of aromatic imines with organic halides.

[reaction: see text] The ortho position of the aromatic ring of imino group substituted aromatic compounds is directly arylated and alkenylated with organic halides in the presence of a catalytic amount of a ruthenium(II)-phosphine complex.

Asymmetric 1,4-addition of organosiloxanes to alpha,beta-unsaturated carbonyl compounds catalyzed by a chiral rhodium complex.

Highly enantioselective 1,4-addition of organosiloxanes to alpha,beta-unsaturated carbonyl compounds was found to be catalyzed by a chiral rhodium complex generated from [Rh(cod)(MeCN)(2)]BF(4) and (S)-BINAP. Both (E)- and (Z)-1-alkenyl groups as well as aryl groups can be introduced enantioselectively into the beta-position of a variety of ketones, esters, and amides. [reaction--see text]

Pd-catalyzed ß-selective direct C-H bond arylation of thiophenes with aryltrimethylsilanes.

Direct arylation of thiophenes and benzothiophenes with aryltrimethylsilanes was effectively catalyzed by PdCl(2)(MeCN)(2) in the presence of CuCl(2) as an oxidant. The reaction preferentially occurred at the ß-position of both thiophenes and benzothiophenes.

Rhodium-catalyzed asymmetric coupling reaction of allylic ethers with arylboronic acids.

An asymmetric allylic substitution of simple allylic ethers with arylboronic acids in the presence of a rhodium(I)/(R)-DTBM-SEGPHOS catalyst has been developed. The reactions proceeded smoothly at room temperature to give the corresponding branch products with excellent regioselectivities and good to excellent enantioselectivities.

Rh-catalyzed reductive coupling reaction of aldehydes with conjugated dienes promoted by triethylborane.

Rh(I) catalyzes the reductive coupling reaction of a wide variety of aldehydes with conjugated dienes in the presence of a stoichiometric amount of triethylborane to provide homoallyl alcohols in a single operation.

Ortho-selective direct cross-coupling reaction of 2-aryloxazolines and 2-arylimidazolines with aryl and alkenyl halides catalyzed by ruthenium complexes.

The ortho position of the aromatic ring in 2-aryloxazolines and 2-arylimidazolines is selectively arylated and alkenylated with organic halides in the presence of a ruthenium(II)-phosphine complex. In the case of unsubstituted and para-substituted phenyloxazolines, 1:2 coupled products were obtained preferentially, while 1:1 coupled products were obtained in the case of meta-substituted phenyloxazolines and N-acylarylimidazolines. The reaction is proposed to proceed via the generation of an organoruthenium intermediate, formed by oxidative addition of the organic halide, and ortho-ruthenation directed by the coordination of the 2-oxazolinyl or 2-imidazolinyl group to the ruthenium center.